1. Technical Field
The present invention relates to a screen, a rear projector, and an image display device.
2. Related Art
In recent years, a projector has been rapidly spread. In addition to a front projection type projector that is mainly used for a presentation, a rear projection type projector has been increasingly recognized as a large-screen projector. A projection type display device is advantageous in that it can provide a product having the same screen size at a low cost, as compared with a direct-view-type display, such as a liquid crystal television or a PDP. However, the direct-view-type display device has become inexpensive, and a high image quality has been required in the projection type display device.
A projector radiates light emitted from a light source onto a light modulating element, such as a liquid crystal light valve, projects the projection light modulated by the light modulating element onto a screen, and displays an image on the screen. When the image is displayed on the screen, so-called scintillation occurs in which an entire surface of the screen flickers.
In this case, a scintillation occurrence principle will be described with reference to FIGS. 12A and 12B.
As shown in FIGS. 12A and 12B, light emitted from a light source 70 passes through liquid crystal light valves, and is then projected onto a screen 74 including a diffusion member 72. The projection light that is projected onto the screen 74 is diffused by the diffusion member 72 included in the screen 74. The diffused light is diffracted by the diffusion member 72 at the time of passing through the screen, and acts like a two-dimensional wave. As shown in FIG. 12B, two spherical waves by the two-dimensional wave are intensified or weakened according to a phase relationship between the two waves, and appears as an interference fringe between a surface of the screen and a viewer. If the viewer focuses on an image surface S where the interference fringe is generated, the viewer recognizes the interference fringe as scintillation that causes the screen surface to flicker.
The scintillation gives unpleasantness to a viewer viewing the image formed on the surface of the screen, as if a veil, a cloth, or a cobweb extends between the screen surface and the viewer. Further, the viewer becomes view a double image like the screen surface and the scintillation through eyes, and focuses on each of the screen surface and the scintillation. As a result, the viewer feels fatigued.
In recent years, instead of a high pressure mercury lamp as a light source of a projector, it is required for a new light source to be developed. In particular, the laser light source has been anticipated as a light source for a next-generation projector, in terms of energy efficiency, color reproducibility, a long life span, instantaneous lighting, or the like. However, instead of a high pressure mercury lamp as a light source of a projector, when using a laser light source causing high interference, contrast of the interference fringe becomes higher, it becomes hard to endure unpleasantness or fatigue due to scintillation.
Accordingly, various technologies for reducing the scintillation have been suggested.
For example, JP-A-11-38512 discloses a screen which includes an emissions-side light diffusion layer that is formed of a plastic material where a light diffusion material is mixed, a middle layer that is formed of a transparent plastic material, and an incidence-side light diffusion layer that is formed of a plastic material where a light diffusion material is mixed. According to this screen, the scintillation that occurs due to the incident-side light diffusion layer is diffused again by the emission-side light diffusion layer, which reduces the occurrence of the scintillation.
Further, JP-A-2001-100316 and JP-A-2001-100317 disclose screens for image projection in which at least one layer of light diffusion layers forming the screen for image projection is caused to vibrate therein, and thus relative positional relationships between the light diffusion layers are varied. As such, an internal vibration is applied to the light diffusion layers, which reduces the occurrence of the scintillation.
However, according to the methods of reducing scintillation that are disclosed in JP-A-11-38512, JP-A-2001-100316, and JP-A-2001-100317, the following problems are generated.
According to the method disclosed in JP-A-11-38512, since the emission-side light diffusing layer is fixed, a phase distribution in a space between a screen and a viewer, which is formed by interference between light rays emitted from respective points on a diffusion surface, is fixed, and an interference fringe is also viewed as a fixed image. Accordingly, there is a problem in that it is not possible to reduce the scintillation.
According to the methods disclosed in JP-A-2001-100316 and JP-A-2001-100317, since various vibration means, such as light, an electric field, a magnetic field, a heat, or a stress, are used, an extra driving energy is needed. Further, when using the vibration means, efficiency of an energy transmitted to a diffusion layer is low, and it becomes difficult for a viewer to comfortably view a screen due to vibrations, sounds, unnecessary electromagnetic waves, exhaust heat, or the like. Further, when the diffusion layer vibrates in a z direction (focus direction), since an image height is varied, and a location of an outline of the image in the x-y direction is also varied, which causes a defocus.